7. Project Summary/Abstract Dopamine (DA) neurotransmission is vital for behaviors such as movement and reward, as well as, cognitive functions including mood, learning and memory. Several neuropsychiatric disorders are linked to alterations in DA signaling including Attention Deficit Hyperactivity Disorder (ADHD), schizophrenia, Parkinson's disease, and addiction. The DA transporter (DAT) is imperative for temporal and spatial control of DA signaling. DAT is located at the presynaptic terminal of DAergic neurons and facilitates the termination of DAergic transmission by rapidly clearing released DA. DAT is the primary target of addictive and therapeutic psychostimulants, which compete for DA binding and block uptake through the transporter, preventing DA clearance and leading to the hyper-locomotive and rewarding behaviors associated with drug use. Given that DAergic signaling is highly sensitive to DAT function, understanding the molecular mechanisms that control DAT function and availability is a critical missing piece of the puzzle in understanding DAergic neurotransmission and dysfunction in DA- related disorders. Over two decades of research support that DAT surface expression is acutely regulated by endocytic trafficking. Protein kinase C (PKC) activation with phorbol esters stimulates DAT internalization and thereby decreases DAT surface expression and function. Although considerable progress has been made to define the molecular mechanisms governing basal and PKC-regulated DAT trafficking, there are significant gaps in our understanding of this process in bona fide DAergic terminals. It is not clear how DAT is regulated in response to the endogenous presynaptic receptors that are activated upstream of PKC, such as Gq-coupled receptors, and how the complex signal events stemming from Gq receptor activation integrate to acutely control DAT surface expression. It is additionally unknown whether regulated DAT trafficking is region-specific, or whether altered DAT surface expression impacts DAergic signaling in the striatum. The proposed studies will leverage chemogenetic receptors to test how Gq activation impacts DAT surface levels in a cell- autonomous manner, in both dorsal and ventral striatum. We will capitalize on a novel conditional, inducible, in vivo gene silencing approach to determine the endocytic mechanisms that are required for Gq-mediated DAT trafficking, by both chemogenetic and endogenous presynaptic receptors. We will further employ ex vivo fast- scan cyclic voltammetry to investigate how presynaptic DAT trafficking impacts DA signaling. I anticipate that at the completion of these studies, we will have gained a more in-depth understanding of the complex mechanisms underlying DAT regulation at presynaptic DAergic terminals, and its potential influence on synaptic DA homeostasis.